Method of sterilizing medical grade film

ABSTRACT

A medical grade film, a method of sterilizing a medical grade film and the sterilized medical grade film produced thereby, wherein the film contains a vinyl chloride resin, such as PVC, and barium sulfate. The film can be sterilized by exposure to gamma radiation of one to five megarads without any color change. Electron beam radiation may also be employed.

This is a continuation of application Ser. No. 07/037,043, filed Apr.10, 1987, now U.S. Pat. No. 4,839,233, issued June 13, 1989.

BACKGROUND OF THE INVENTION

This invention pertains to medical grade film and a method ofsterilizing medical grade film and, more particularly, to medical gradefilm and a method of sterilizing the same wherein the film can be gammaor electron beam sterilized without any color change, and the sterilizedmedical grade film produced thereby.

Medical grade film, e.g., film meeting the requirements of Class VIplastics as set forth in the U.S. Pharmacopeia, Volume XX, is useful formanufacturing products which can be used for medical treatments and formanufacturing containers for products such as pharmaceuticals, cosmeticsand foods. Suitable applications for such films are enteric feedingbags, kidney dialysis bags, barium enema bags, colostomy bags,bloodwashing bags, blood storage bags, urinary drainage bags,incontinent products, inflatable splints, hospital I.D. bracelets,traction devices, burn mattresses, comfort cushions and waterproofhospital sheeting.

Currently, the medical industry utilizes a medical grade film containingpolyvinyl chloride (PVC) resin. The industry sterilizes this medicalgrade film using ethylene oxide. However, this is a cumbersome,time-consuming and expensive method of sterilization. The industryprefers using the gamma-radiation sterilization method since it is moreeffective biologically, less expensive and less time-consuming. However,irradiation levels of 1 to 5 megarads used in this sterilization methodcause the polyvinyl film to yellow. While this yellowing does not renderthe film nonfunctional, it is considered undesirable aesthetically.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amedical grade film which may be gamma or electron beam sterilizedwithout any color change.

It is a further object of the present invention to provide a method ofsterilizing a medical grade film with gamma or electron beam radiationwithout any color change in the film.

It is an additional object of the present invention to provide asterilized medical grade film.

These objects are accomplished by providing a halogen containing resinfilm including barium sulfate. The halogen containing resin ispreferably a vinyl chloride resin such as PVC. In addition to polyvinylchloride and barium sulfate, the film can also contain a plasticizersuch as di-2-ethylhexyl adipate, epoxidized soybean oil, a stabilizersuch as an orango zinc soap blend or an organotin salt, and a lubricantsuch as stearic acid.

The medical grade film of the present invention can be successfullygamma or electron beam sterilized without any color change. For example,gamma radiation doses can range from 1 to 5 megarads.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A medical grade film of the present invention includes a halogencontaining resin and, more particularly, a vinyl chloride resin. Thevinyl chloride resin may be a homopolymer of vinyl chloride or a mixedpolymer, such as copolymers or graft polymers of vinyl chloride whichhave been prepared by known continuous or batch polymerizationprocesses. Suitable monomers for copolymerization with vinyl chlorideare olefins, vinyl esters of carboxylic acids, acrylonitrile, styreneand cyclohexylmaleimide. Polymers useful for graft polymerization withvinyl chloride include elastomeric polymers of butadiene, ethylene,propylene, styrene and/or acrylonitrile.

The medical grade film of the present invention may contain any of anumber of known stabilizers. Suitable stabilizers include organo zincsoap blends and metallic soaps of calcium and zinc. A preferablestabilizer is Mark QTS (an organo zinc soap blend manufactured by ArgusChemical Division of Witco Chemical Corp.).

The medical grade film of the present invention may contain any of anumber of known lubricants. Such lubricants include calcium stearate,hydrogenated tallow and fatty acids (food grade): Preferable lubricantsinclude stearic acid and calcium stearate.

Known plasticizers may also be included in the medical grade film of thepresent invention. Examples of such plasticizers are phthalateplasticizers such as dioctyl phthalate (D.O.P.). However, the preferredplasticizer is di-2-ethylhexyl adipate.

The medical grade film may contain other additives such as epoxidizedsoybean oil and FDA approved pigments.

The advantageous effects of the present invention are obtained byincluding barium sulfate in the medical grade film.

The foregoing raw materials are preferably included in the medical gradefilm of the present invention in the following proportions by weightpercent: the amount of PVC resin preferably contained in the compositionis 60 to 69%; the amount of plasticizer is preferably 19 to 25%; theamount of stabilizer is preferably 0.5 to 1.3%; the amount of lubricantis preferably 0.15 to 0.2%; the amount of epoxidized soybean oil ispreferably 9.5 to 10.5%; and the amount of barium sulfate is preferably0.5 to 5%, most preferably 2.9%.

The raw materials can be mixed by blending then Banburying. Thecomposition obtained thereby can then be calendered to form films havinga thickness in the range of 2 to 30 mils, preferably 6 to 18 mils.

The films can be shaped by known techniques such as electronic heatsealing to form useful articles.

Sterilization is preferably accomplished by exposing the films or shapedarticles to gamma radiation. Gamma radiation sources are known in theart, e.g., a cobalt 60 source may be used. Typical irradiation levelsare in the range of 1 to 5 megarads. Electron beam radiation may also beemployed.

EXAMPLE 1

A film was prepared by blending the following raw materials followed byBanburying and calendering:

PVC resin--100 parts by weight,

Di-2-ethylhexyl adipate (DOA plasticizer)--33 parts by weight,

Mark QTS (an organo zinc soap blend manufactured by Argus ChemicalDivision of Witco Chemical Corp.)--0.75 parts by weight,

Drapex 6.8 (epoxidized soybean oil manufactured by Argus ChemicalDivision of Witco Chemical Corp.)--15 parts by weight,

Barium sulfate--4.47 parts by weight, and

Industrene 7018 FG (Food Grade 70% stearic acid manufactured by HumkoChemical Division of Witco Chemical Corp.)--0.25 parts by weight.

The film was successfully sterilized using 1 to 5 megarads of gammaradiation without any color change.

Large scale processing of the film can be accomplished in the followingmanner. The PVC resin can be stored in resin silos. Bulk plasticizersuch as D.O.P. and epoxidized soybean oil can be stored in separateplasticizer tanks. Bulk PVC resin, D.O.P. and epoxidized soybean oil canbe pumped and weighed into blenders. The other ingredients, such aslubricants and barium sulfate, can be kept in drums and/or bags and canbe weighed into the blender. The total weight of the raw materials inthe blender can be approximately 4,000 lbs. These materials are thenblended for 25 minutes at approximately 200° F.

Two-hundred-fifty pounds of the blended raw materials are thentransferred into the Banbury where the materials are mixed for 31/2minutes, reaching a temperature of 340° F., until the formulation isfused. The plastic formulation is then transferred to a two-roll millwhich is at a temperature of 320° F. This mill performs the function ofmixing and storage.

The material is then transferred to an extruder-strainer which is at atemperature of 325° F. The material is strained and extruded into acontinuous web approximately 3 inches in diameter which is fed to acalender. A calender, such as a four-roll inverted-L calender, can beused. The calender rolls are heated, top to bottom, from 350° F. to 310°F. The calender forms the (webbed) material into a sheet of variouswidths and thickness. The calender sheet is then cooled by cooling drumsand a beta gauge measures the thickness of the sheet. A winder rolls thesheet into a roll which is then slit into smaller rolls on a slitter.The rolls can then be packaged into, e.g., a polyethylene bag which iswrapped with Kraft paper. The thus-formed medical grade film can be usedto fabricate desired products by conventional electronic heat sealingequipment. The film or products can be sterilized using gamma orelectron beam radiation.

While the invention has been described and illustrated by the exampleincluded herein, it is not intended that the invention be strictlylimited thereto, and other variations and modifications may be employedwithin the scope of the following claims.

What is claimed is:
 1. A method of sterilizing a medical grade filmcomprising exposing the film to high energy radiation, wherein the filmcomprises a vinyl chloride resin containing sufficient barium sulfate toprevent discoloration of said film when exposed to said radiation. 2.The method of sterilizing a medical grade film according to claim 1,wherein said high energy radiation is gamma radiation or electron beamradiation.
 3. The method of sterilizing a medical grade film accordingto claim 2, wherein said vinyl chloride resin is polyvinyl chloride. 4.The method of sterilizing medical grade film according to claim 2,wherein said film is irradiated with one to five megarads of gammaradiation.
 5. The method of sterilizing medical grade film according toclaim 3, wherein said film further comprises a plasticizer.
 6. Themethod of sterilizing medical grade film according to claim 5, whereinsaid plasticizer is di-2-ethylhexyl adipate.
 7. The method ofsterilizing medical grade film according to claim 5, wherein said filmfurther comprises epoxidized soybean oil, a stabilizer and a lubricant.8. The method of sterilizing medical grade film according to claim 1,wherein said medical grade film consists essentially of polyvinylchloride, di-2-ethylhexyl adipate, an organo zinc soap blend, epoxidizedsoybean oil, stearic acid and barium sulfate.
 9. The method ofsterilizing medical grade film according to claim 1, wherein said filmhas a thickness in the range of 2-30 mils.
 10. The method of sterilizingmedical grade film according to claim 1, wherein said film has athickness in the range of 6-18 mils.
 11. The method of sterilizingmedical grade film according to claim 5, wherein said film has athickness in the range of 2-30 mils.
 12. The method of sterilizingmedical grade film according to claim 5, wherein said film has athickness in the range of 6-18 mils.
 13. The method of sterilizingmedical grade film according to claim 1, wherein said medical grade filmconsists essentially of 60-69 wt. % polyvinyl chloride, 19-25 wt. %plasticizer, 0.5-1.3 wt. % stabilizer, 0.15-0.2 wt. % lubricant,9.5-10.5 wt. % epoxidized soybean oil, and 0.5-5 wt. % barium sulfate.14. The method of sterilizing medical grade film according t claim 13,wherein the amount of said barium sulfate is 2.9 wt. %.